JP2001054083A - Attenuator for cable modem - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain the reception for a cable modem at a prescribed receiving level and also to evade attenuation of the transmitting signals of the modem. SOLUTION: A plug part 10b connectable to a coaxial connector is prepared at one of both ends of a main body part 10a of an attenuator 10 used for a cable modem with a plug part 10c connectable to a coaxial plug prepared at the other end of the part 10a respectively. A printed circuit board 30 where an attenuator circuit is built in is stored into a space part included in the part 10a. Thus, the attenuator 10 is attached to the cable modem to attenuate the signals received from a network at a prescribed level. Under such conditions, the signals transmitted from the cable modem are never attenuated by the attenuator 10 and can be transmitted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an attenuator for a cable modem which can transmit and receive at an appropriate level by a cable modem in a CATV system.

[0002]

2. Description of the Related Art In recent CATV systems, a cable modem is connected to a cable television network, and a personal computer is connected to the cable television network via the cable modem to use various network services. ing. FIG. 7 shows an example of such a CATV system. C shown in FIG.
The CATV center 51 in the ATV system 200
A variety of program signals and various data are transmitted from a head end 51a provided to the main line constituting a plurality of cable television networks. Various program signals and various data transmitted to the main line are propagated through the main line, and bidirectional main line amplifiers (AMP) 52a, 52b provided at predetermined distances.
, And the frequency characteristics are equalized and propagated.

[0003] This trunk line is branched in some places by a branch amplifier or a branching device, propagates through the branch trunk line, is further distributed by a distributor, and passes through tap-offs 53a and 53b.
It is drawn into each facility and each home via the protectors 54a and 54b. Thereby, each facility and each home can receive various program signals and various data. Home terminals 55a and 55 are provided at each facility and each home.
b, and the home terminals 55a, 55b
, Various program signals are decoded or selected. Thus, a desired program can be enjoyed by the televisions 57a and 57b connected to the home terminals 55a and 55b.

Further, in order to connect the personal computers 58a and 58b installed in each facility and each home to the cable television network, the personal computers 58a and 58b are connected to the cable television network via the cable modems 56a and 56b. In this case, for example, the upstream signal transmitted when connecting to the Internet from the personal computers 58a and 58b goes to the CATV center 51 via the cable modems 56a and 56b and the cable television network, and is provided to the CATV center 51. It is sent to the Internet provider 59 via the router 51b. As a result, the personal computers 58a and 58b installed in each facility and each home are connected to the Internet via the Internet provider 59, and can receive Internet services. Also, CATV
When the center 51 can provide another network service, the personal computers 58a and 58b installed in each facility and each home are connected to the network in the same manner.

[0005]

By the way, the upstream frequency band in a cable television network is slightly different depending on the cable modem, but is 5 to 55 MHz, and the downstream frequency band is 70 to 770 MHz. The transmission level of the cable modems 56a and 56b, that is, the upstream signal level is 68 to 118d depending on the specification.
BμV, and the reception signal level, that is, the downstream signal level is 45 to 75 dBμV according to the specification. On the other hand, the level of various program signals in the cable television network is set to 60 to 90 dBμV. The various program signals are of course the level of the downstream signal, and the amplifier inserted into the cable television network amplifies and propagates the downstream signal so that the level of the downstream signal is secured. .

[0006] Then, the level of the downstream signal directed to the personal computers 58a and 58b installed in each facility and each home is also set to a level of 60 to 90 dBμV, like the various program signals, and propagated on the network. Therefore, the personal computer 58 received by the cable modems 56a and 56b
a, the level of the downstream signal toward 58b is also 60 to 90 dB
μV level, the cable modems 56a, 56b
Of the received signal becomes excessive, and the cable modems 56a and 56b may cause a data error. To prevent this, the cable modem 56
An attenuator may be inserted before a and 56b to lower the received signal level. However, since the attenuator lowers the level over all frequency bands, the level of the transmission signal of the cable modems 56a and 56b is also reduced. There is a problem that it is.

It is an object of the present invention to provide an attenuator for a cable modem that allows a cable modem to receive a signal at a prescribed reception level and does not attenuate a transmission signal.

[0008]

In order to achieve the above object, a cable modem attenuator according to the present invention is provided at one end with a plug portion connectable to a coaxial connector and at the other end with a coaxial plug connectable. A cylindrical body provided with a connector portion; and a printed circuit board in which an attenuator circuit is housed in a space inside the body portion. One end of the attenuator circuit incorporated in the printed circuit board is connected to one terminal of the attenuator circuit, and an end of the center contact in the connector portion is connected to another terminal of the attenuator circuit incorporated in the printed circuit board.

In the attenuator for a cable modem according to the present invention, the attenuator may be inserted between the cable modem and the network cable to attenuate only the level of the frequency band of the downstream signal. Further, in the attenuator for a cable modem according to the present invention, the attenuator circuit is disposed after the high-pass filter that passes a down signal, a low-pass filter that passes an up signal provided in parallel with the high-pass filter, and the high-pass filter. And the high-pass filter and the low-pass filter have Butterworth characteristics.

[0010] According to the present invention, since the plug is of a plug type in which a plug portion connectable to a coaxial connector is provided at one end and a connector portion connectable to a coaxial plug is provided at the other end. It can be directly attached to the coaxial connector provided in the modem, and can be easily installed without requiring an installation place. Further, since the attenuator circuit is configured to attenuate only the level in the frequency band of the downstream signal, the received signal level can be attenuated to the specified level without attenuating the transmission signal level.

Further, a filter is incorporated in the attenuator circuit to attenuate only the level of the frequency band of the downstream signal. However, since the filter is of a plug type, the filter must be formed because the attenuator circuit needs to be downsized. It is necessary to use a chip inductor for the coil. But,
Since the inductance cannot be adjusted after the chip inductor is incorporated in the circuit, the filter of the attenuator circuit according to the present invention has a Butterworth characteristic to reduce the influence on Q (selectivity) even if the inductor changes with temperature. This makes it difficult to affect the filter characteristics.

[0012]

FIG. 2A shows an example of the configuration of an attenuator for a cable modem according to an embodiment of the present invention.
(B) and (c). 2 (a) is a front view of the cable modem attenuator 10 of the present invention, FIG. 2 (b) is a side view thereof, and FIG. 2 (c) is a sectional view showing the internal configuration thereof. As shown in FIGS. 2A to 2C, the cable modem attenuator 10 according to the present invention includes:
Conductive cylindrical body 10a made of, for example, metal
And a plug portion 10b connected to a coaxial connector provided at one end thereof, and a connector portion 10c connected to a coaxial plug provided at the other end. The metal plug portion 10b is rotatably fixed to the main body portion 10a, and a screw screwed to the coaxial connector is formed on the inner peripheral surface thereof, and the outer periphery thereof is rotated with a tool such as a spanner. It has a hexagonal shape so that it can be made.

One end of the main body 10a has a reduced diameter and is extended. A first insulator 10f is fitted inside the main body 10a, and a center conductor 10d is inserted through the center of the first insulator 10f. I have. The center conductor 10d is connected to the plug 10b.
And a center conductor 10d in the plug portion 10b.
It has been. Further, a fitting ring 10e is fitted between the tip end of the main body 10a, which is reduced in diameter and extends, with the inner peripheral surface of the plug 10b to perform positioning and rotation control of the plug 10b. ing. On the other hand, a metal connector 10c is fitted to the other end of the main body 10a,
A cylindrical second insulator 10h is fitted into the connector portion 10c. A center contact 10g is arranged at the center of the second insulator 10h. Center contact 10
g is a portion where the center conductor of the coaxial plug is inserted and connected when the coaxial plug is connected.

Further, a printed circuit board 30 on which an attenuator circuit is assembled is housed in the main body 10a. A rear end of the center conductor 10d is connected to one terminal of the printed circuit board 30 by soldering or the like. The rear end of the center contact 10g is connected to the other terminal of the substrate 30 by soldering or the like. Thus, the attenuator circuit is connected between the center conductor 10d and the center contact 10g. The attenuator circuit is incorporated on one surface of the printed circuit board 30 mainly using chip components. As described above, the cable modem attenuator 10 according to the present invention is of the plug type in which the attenuator circuit is housed inside the plug.

FIG. 3 shows an example of an attenuator circuit incorporated in the printed circuit board 30. The attenuator circuit shown in FIG. 3 will be described from the input terminal IN side.
Is a coil for impedance matching, and this coil L
1 branches into two circuits connected in parallel. In one circuit, a first high-pass filter (HPF1), an attenuator (ATT), and a second high-pass filter (HPF2) are cascaded. The other circuit is a low-pass filter (LPF). First high-pass filter (HP
F1) includes capacitors C1, C2, C3 and coil L2,
A T-type filter composed of L3 is a Butterworth characteristic filter connected in cascade in two stages. This filter is
70-7 which is the frequency band of the signal received by the cable modem
The cut-off frequency is designed to be 70 MHz so that it can pass at least 70 MHz. The second high-pass filter (HPF2) includes capacitors C4, C5,
A T-type filter composed of C6 and coils L4 and L5 is a Butterworth characteristic filter that is cascaded in two stages. This filter is also designed to have a cut-off frequency of 70 MHz so that it can pass at least 70 to 770 MHz, which is the frequency band of the signal received by the cable modem.

The attenuator has resistors R1, R2 and R3 of π.
It is a π-type attenuation circuit connected to the mold. Then, the first high-pass filter (HPF1) and the attenuator (AT
T) and the second high-pass filter (HPF2) have a pass loss characteristic of attenuating about 13 dB in a frequency band of 70 MHz to 770 MHz.
The capacitor C7 in the other circuit is a DC cut capacitor, and a low-pass filter (LPF) composed of coils L6, L7, L8, L9 and capacitors C8, C9, C10 has three T-type filters connected in cascade. The filter has a Butterworth characteristic, and has a pass band through which the frequency band of 5 to 55 MHz of the transmission signal of the cable modem can be passed without attenuation.

The capacitor C11 is a DC cut capacitor, and the two parallel circuits are connected to the output terminal OUT via the capacitor C11. The input terminal IN is connected to a cable television network via a connector 10c having a center contact 10g to which the input terminal IN is connected, and the output terminal OUT is a center conductor 10d to which the output terminal OUT is connected.
Is connected to the coaxial connector of the cable modem via the plug section 10b having The frequency characteristics of the attenuator 10 for a cable modem having such an attenuator circuit are such that a signal in a frequency band of 5 to 55 MHz passes without being attenuated, and a signal having a frequency of 70 to 55 MHz.
The signal in the 770 MHz frequency band has a frequency characteristic of attenuating about 13 dB. Thus, when the cable modem attenuator 10 is inserted immediately before the cable modem, the transmission signal of the cable modem, which is the upstream signal, is passed without attenuating, and the downstream signal is attenuated by about 13 dB and received by the cable modem. Become.

The first high-pass filter (HPF1)
The reason why the second high-pass filter (HPF2) and the low-pass filter (LPF) have Butterworth characteristics is as follows. Attenuator for cable modem 10
Is a plug type, so that the attenuator circuit cannot be housed in the main body 10a unless the attenuator circuit is downsized. Therefore, it is necessary to reduce the size of the attenuator circuit mainly by using chip components, and the coil constituting the filter must use a chip inductor. However, unlike the air-core coil, the inductance of the chip inductor cannot be adjusted after being incorporated in the circuit. Therefore, the filter of the attenuator circuit according to the present invention is used as Butterworth characteristics to reduce the influence on Q (selectivity) even if the inductance of the chip inductor slightly changes due to temperature, thereby making it difficult to affect the filter characteristics. is there.

Next, FIG. 4 shows a pattern on the printed circuit board 30 in which the attenuator circuit shown in FIG. 3 is incorporated. Since the printed circuit board 30 is housed in the main body 10a shown in FIG. 2, it has an elongated shape so as to match the internal space shape of the main body 10a. Since the area of the internal space is small, chip components are mainly used so that the occupied area of each element incorporated in the printed circuit board 30 shown in FIG. 4 is reduced. That is, the capacitors C1 to C1
A chip capacitor is used up to the capacitor C10, and a chip inductor is used up to the coils L2 to L9. However, the coil L1 is an air-core coil.

The printed circuit board 30 has an input terminal IN
The center contact 10g is soldered to the pattern 31 forming the main body 10a by connecting the center conductor 10d to the pattern 32 forming the output terminal OUT.
Is fixed inside. Further, the protruding portions 30a on both sides of the printed board 30 are soldered to the ends of the connector 10c facing the inside of the main body 10a, so that the ground pattern of the printed board 30 is connected to the main body 10a. The printed circuit board 30 is more firmly
0a.

In the attenuator circuit shown in FIG. 5 configured as described above, the capacitors C1 and C6 are connected by approximately 20P.
F, approximately 15 PF for capacitors C2 and C5, capacitor C
3, C4 is approximately 39PF, resistors R1 and R3 are approximately 120Ω,
The resistance R2 is approximately 160Ω, the coil L2 is approximately 0.1 μH, the coils L3 and L4 are approximately 0.12 μH, and the coil L5 is approximately 0.1 μH.
15 μH, capacitors C7 and C11 are approximately 1000 PF,
Capacitors C8 and C10 are approximately 47 PF, and capacitor C9
FIG. 5 shows the frequency characteristics of the attenuator 10 for a cable modem in the case where is approximately 43 PF, the coils L6 and L9 are approximately 0.33 μH, and the coils L7 and L8 are approximately 0.48 μH. Referring to FIG. 5, the attenuation is set to about 2 dB or less in an upstream frequency band of 5 to 55 MHz, and 70 to 770 MHz.
Since the attenuation is about 13 dB or more in the frequency band downstream of z, the cable modem attenuator 10
Is inserted immediately before the cable modem, the transmission signal of the cable modem, which is the upstream signal, is passed with almost no attenuation, and the downstream signal is attenuated by approximately 13 dB and received by the cable modem. As a result, the transmission signal of the cable modem can be transmitted without attenuating, and the cable modem can receive the signal at a reception level without causing a data error.

FIG. 6 shows VSWR (voltage standing wave ratio) characteristics when the value of each element in the attenuator circuit shown in FIG. 3 is set to the above constant. Referring to FIG.
A good VSWR of about 1.7 or less in an up-frequency band of about 55 MHz and a VSWR of about 1.3 or less in a down-frequency band of 70 to 770 MHz.
Attenuator 10 for cable modem
It can be seen that and the cable TV network are well matched over the entire area. The coil L1 for impedance matching has a winding diameter of approximately 1.5 mmφ,
The wire diameter is approximately 0.4 mmφ, the number of turns is approximately 1.5 turns, and the coil L1 is adjusted so that the VSWR is good.

FIG. 1 shows a configuration example of a CATV system when the above-described cable modem attenuator 10 according to the present invention is applied to a CATV system. In the CATV system 100 shown in FIG.
A variety of program signals and various data are transmitted from the head end 1a provided to the main line constituting a plurality of cable television networks. The various program signals and various data transmitted to the main line are propagated along the main line, amplified by the bidirectional main line amplifiers (AMP) 2a and 2b provided at predetermined distances, and transmitted with equalized frequency characteristics. Go.

This trunk line is branched into branch trunk lines by branch amplifiers and branch devices and propagates along the branch trunk line, and is further distributed by the distributors, via tap-offs 3a and 3b, and via protectors 4a and 4b. To be drawn into each facility and home. Thereby, each facility and each home can receive various program signals and various data. Home terminals 5a and 5b for each facility and home
Are provided, and various program signals are decoded or selected in the home terminals 5a and 5b. Thereby, a desired program can be enjoyed by the televisions 7a and 7b connected to the home terminals 5a and 5b.

Further, personal computers 8a and 8b installed in facilities and homes are connected to the cable television network, and the personal computers 8a and 8b are connected to the cable modems 6a and 8b.
6b. In addition, the protectors 4a, 4b
Coaxial cable and cable modem 6a,
The cable modem attenuators 10, 10 according to the present invention are inserted between 6b. Specifically, the cable modem attenuator 1 is connected to a coaxial connector for connecting coaxial cables provided in the cable modems 6a and 6b.
The cable modem attenuators 10 and 10 are connected by screwing the 0 plug portion 10b.

As described above, when the cable modem attenuator 10 is attached to the cable modems 6a and 6b, the transmission signals of the cable modems 6a and 6b, which are the upstream signals, are transmitted without attenuation, and transmitted. The received signal, which is a downlink signal, is attenuated by about 13 dB and is received by the cable modems 6a and 6b. Therefore, the cable modems 6a and 6b receive the reception signal at a prescribed level.
a, 6b is prevented from causing a data error. Further, the transmission signals from the cable modems 6a and 6b are transmitted at a specified transmission level without being attenuated. Further, attenuators 10, 1 for cable modems are connected to coaxial connectors provided in the cable modems 6a, 6b.
0 can be directly attached, so that it can be easily installed without requiring an installation place.

The thus configured CATV system 1
At 00, for example, a transmission signal transmitted from the personal computer 8a when the personal computer 8a is connected to the Internet is transmitted from the cable modem 6a without being attenuated via the cable modem 6a, the cable modem attenuator 10, and the protector 4a. At the specified transmission level to the CATV center via the cable television network. Then, in the CATV center 1, the data is transmitted to the Internet provider 9 via the provided router 1b. In this way, the personal computer 8a installed in the facility or home is connected to the Internet via the Internet provider 9.

Then, various data taken in through the Internet provider 9 are transmitted to the C through the router 1b.
The data is taken into the ATV center 1 and transmitted from the head end 1a to the main line. As a result, the cable modem attenuator 10 through the cable television network and the tap-off 3a and the protector 4a provide about 13
The signal is received by the cable modem 6a at a prescribed reception level which does not cause a data error by being attenuated by dB.
Thus, the personal computer 8a is connected to the Internet and can receive Internet services. Similarly, the personal computer 8b has a cable modem 6b.
And it becomes possible to connect to the Internet via the cable modem attenuator 10. Also,
When the CATV center 1 can provide another network service, the personal computers 8a and 8b installed in each facility and each home can be connected to the network in the same manner.

[0029]

As described above, the present invention is of a plug type in which a plug portion connectable to a coaxial connector is provided at one end and a connector portion connectable to a coaxial plug is provided at the other end. Can be directly attached to the coaxial connector provided in the cable modem, and can be easily installed without requiring an installation place. Also,
Since the attenuator circuit is configured to attenuate only the level of the frequency band of the downstream signal, it is possible to attenuate the received signal level to a specified level without attenuating the transmission signal level.

Further, a filter is incorporated in the attenuator circuit to attenuate only the level of the frequency band of the downstream signal. However, since the filter is of the plug type, the filter must be formed because it is necessary to reduce the size of the attenuator circuit. It is necessary to use a chip inductor for the coil. But,
Since the inductance cannot be adjusted after the chip inductor is incorporated in the circuit, the filter of the attenuator circuit according to the present invention has a Butterworth characteristic to reduce the influence on Q (selectivity) even if the inductor changes with temperature. This makes it difficult to affect the filter characteristics.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration example of a CATV system when a cable modem attenuator according to the present invention is applied to a CATV system.

FIG. 2 is a diagram illustrating an example of a configuration of an attenuator for a cable modem according to an embodiment of the present invention.

FIG. 3 is a diagram showing an attenuator circuit assembled on a printed circuit board of an attenuator for a cable modem according to an embodiment of the present invention.

FIG. 4 is a diagram showing a pattern of a printed board of the attenuator for the cable modem according to the embodiment of the present invention.

FIG. 5 is a diagram illustrating attenuation characteristics of the attenuator for the cable modem according to the embodiment of the present invention;

FIG. 6 is a diagram showing VSWR characteristics of the attenuator for the cable modem according to the embodiment of the present invention.

FIG. 7 is a diagram showing a conventional configuration example of a CATV system.

[Explanation of symbols]

1 Center 1a Headend 1b Router 3a, 3b Tap-off 4a, 4b Protector 5a, 5b Home Terminal 6a, 6b Cable Modem 7a, 7b Television 8a, 8b Personal Computer 9 Internet Provider 10 Cable Modem Attenuator 10a Main Unit 10b Plug 10c Connector Part 10d Center conductor 10e Fitting ring 10f First insulator 10g Center contact 10h Second insulator 30 Printed circuit board 30a Projection 31,32 Pattern 51 CATV center 51a Headend 51b Router 59 Internet provider 100 CATV system 53a, 53b Tap off 54a , 54b Protector 55a, 55b Home Terminal 56a, 56b Cable Modem 57a, 57b Television 58a, 58b Con 200 CATV systems C1, C2, C3, C4, C5, C6C7, C8, C
9, C10, C11 capacitors L1, L2, L3, L4, L5, L6, L7, L8, L
9 Coil IN Input terminal OUT Output terminal R1, R2, R3 Resistance

Claims (3)

[Claims] 1. A cylindrical main body provided with a plug portion connectable to a coaxial connector at one end, and a connector portion connectable to a coaxial plug at the other end, and a space inside the main body portion. A printed circuit board in which an attenuator circuit to be housed is incorporated, wherein an end of the center conductor in the plug portion is connected to one terminal of the attenuator circuit incorporated in the printed circuit board, and an end of a center contact in the connector portion. An attenuator for a cable modem, wherein an end is connected to another terminal of the attenuator circuit incorporated in the printed circuit board. 2. The attenuator for a cable modem according to claim 1, wherein the attenuator is inserted between the cable modem and the network cable to attenuate only the level of a frequency band of a downstream signal. 3. The attenuator circuit comprises a high-pass filter that passes a down signal, a low-pass filter that passes an up signal provided in parallel with the high-pass filter, and an attenuator circuit that is provided after the high-pass filter. 2. The attenuator for a cable modem according to claim 1, wherein said high-pass filter and said low-pass filter have Butterworth characteristics.